1. Field of the Invention
The present invention relates generally to the field of medical imaging, and particularly to measuring and marking of the dimensions of internal physiological characteristics. In one particular aspect, the invention provides fluoroscopic guides and methods for modeling the geometry of endoluminal prostheses within curving and/or branching body lumens such as blood vessels.
To properly treat many bodily diseases or abnormalities, certain physiologic characteristics, such as the size of a particular body member, often need to be determined. Examples of therapies which depend on accurate measurements include the treatment of vascular lesions, stenosed regions, and particularly vascular aneurysms, which often require the endoluminal placement of tubular prostheses, such as grafts, stents, stent-grafts, and other structures. Before the prothesis is placed in the vascular anatomy, the size of the lesion is measured so that a properly sized prosthesis can be selected.
Vascular aneurysms are the result of abnormal dilation of a blood vessel, usually resulting from disease and/or genetic predisposition, which can weaken the arterial wall and allow it to expand. While aneurysms can occur in any blood vessel, most occur in the aorta and peripheral arteries, with the majority of aortic aneurysms occurring in the abdominal aorta, usually beginning below the renal arteries and often extending into one or both of the iliac arteries.
Aortic aneurysms are most commonly treated in open surgical procedures where the diseased vessel segment is bypassed and repaired with an artificial vascular graft. While considered to be an effective surgical technique, particularly considering the alternative of a usually fatal ruptured abdominal aortic aneurysm, conventional vascular graft surgery suffers from a number of disadvantages. The surgical procedure is complex and requires experienced surgeons and well equipped surgical facilities. Even with the best surgeons and equipment, however, patients being treated frequently are elderly and weakened from cardiovascular and other diseases, reducing the number of eligible patients. Even for eligible patients prior to rupture, conventional aneurysm repair has a relatively high mortality rate, usually from 2% to 10%. Morbidity related to the conventional surgery includes myocardial infarction, renal failure, impotence, paralysis, and other conditions. Additionally, even with successful surgery, recovery takes several weeks, and often requires a lengthy hospital stay.
In order to overcome some or all of these drawbacks, endovascular prosthesis placement for the treatment of aneurysms has been proposed. Although very promising, many of the proposed methods and apparatus suffer from undesirable limitations. In particular, proper sizing and positioning of endovascular prostheses can be problematic.
Before endoluminal prosthetic deployment, it is necessary to first determine the appropriate size for the prosthesis so that the prosthesis will properly fit within the body lumen. For instance, in the case of vascular aneurysms, it is desirable to determine the length of the aneurysm so that the prosthesis will be long enough to extend through the diseased area of the vessel. In this way, both ends of the prosthesis can be anchored to a healthy vessel wall.
Current methods for determining the length of an effected body lumen employ fluoroscopy. To determine the length of a vessel using fluoroscopy, a catheter is inserted into the vessel and a contrast agent is injected into the vessel through the catheter. The blood flow carries the contrast agent along the vessel so that the vessel can be radiographically imaged with a fluoroscope. The fluoroscope produces a planar (or two dimensional) image of the vessel which can be evaluated to determine the existence of a diseased or abnormal area within the vessel. The length of the diseased or abnormal area is then estimated by measuring the length of the diseased area on the radiographic image. Unfortunately, accurate linear measurement of these complex three dimensional bodies is difficult to provide when using this known technique.
U.S. patent application Ser. No. 08/380,735, filed Jan. 30, 1995, now abandoned (Attorney Docket No. 016380-001600), and Ser. No. 08/435,288, filed May 4, 1995 now U.S. Pat. No. 5,752,522 (Attorney Docket No. 016380-002900), the full disclosures of which are herein incorporated by reference, describe endoluminal methods for directly measuring lumenal lengths and cross-sections which help to avoid the inaccuracy of measuring curving, three dimensional blood vessels with the known two dimensional fluoroscopic process. By introducing direct measurement devices into the curving blood vessels, and by placing radiopaque markers at either end of a vascular region to measure length, or radially expanding a balloon or other occlusion device until flow is substantially blocked to measure cross-section, these direct measurement devices significantly enhance the accuracy of endoluminal measurements.
Although the direct luminal measurement devices and methods described above represent significant advancements in accurate luminal measurements for placement of endoluminal prostheses and other devices, known methods for subsequently positioning those devices based on these measurements still suffer from certain drawbacks. In particular, once measurements have been made and luminal prosthetic deployment is under way, work in connection with the present invention has shown that accurate positioning of even a correctly sized prosthesis can prove difficult. This is particularly true when positioning bifurcated prostheses extending from the abdominal aorta into the two iliac arteries for treatment of an aortoiliac aneurysm. The bifurcated prosthesis will preferably seal off the aneurysm, but will not obstruct flow to the renal or hypogastric arteries. Unfortunately, the geometry of the aortoiliac junction varies widely between patients, and the position of the prosthesis may shift during deployment. The interaction between the flexible or semi-flexible prosthesis and the complex lumenal geometry can be difficult to visualize, making the deployed prosthetic geometry somewhat unpredictable. Further complicating the situation, direct measurement devices are often removed to avoid interfering with prosthetic deployment, leaving the physician with little guidance as deployment progresses. Finally, where planar measurements are made, the scope often distorts the imaged body structures so that even relative measurements taken from different portions of the image, or along different measurement axis, are highly inaccurate.
In light of the above limitations and disadvantages, it is desirable to provide improved methods and devices to guide endoluminal positioning and placement of tubular prostheses. It would be particularly desirable to provide a simple, reliable reference and measurement device for use during fluoroscopically directed, minimally invasive procedures. It would further be desirable if such improved devices and methods were adaptable to the wide variety of vascular geometries exhibited by patients in need of bifurcated or straight endoluminal prostheses.
2. Description of the Background Art
As previously described, methods and apparatus for direct measurement of the length and cross-section of endoluminal lesions are described in co-pending U.S. patent application Ser. No. 08/380,735, and U.S. Pat. No. 5,752,522 (Attorney Docket Nos. 016380-001600 and 016380-002900). A catheter depth gauge and method of use are described in U.S. Pat. No. 5,239,982. A reference scale in the form of adhesive tape having radiopaque measurement markers is commercially available under the tradename LeMaitre Glow 'N Tell Tape from Vascutech, Inc.